1. Field of the Invention
This invention relates generally to material handling grapples and, more specifically, to grapples which operate while suspended from a single line.
2. Prior Art
A typical prior art grapple comprises an upper block having an upper sheave assembly fixedly attached and a lower block having a lower sheave assembly fixedly attached. A series of arms and tines are pivotally attached to the blocks so that relative vertical movement between the upper and lower blocks opens and closes the tines producing a grasping action.
Two lines from an overhead crane are required to operate the aforementioned prior art grapple. A first line is looped between the upper and lower sheave assemblies to form a pulley. The weight of the grapple suspended from the first line draws the upper and lower block together thereby closing the tines about an object to be raised. The second line is connected to the upper block and is slack when an object is grasped. When the object is to be released, the second line is drawn taut and the first line is played out. When the first line is slack, the weight of the lower block causes it to drop away from the upper block thereby opening the tines.
An obvious shortcoming of the prior art grapple is that it can only be operated by a crane having two independently operable lines from which to suspend a grapple. However, because many loading and unloading facilities, especially maritime facilities, have booms with a single line, there is a need for a single line grapple.